<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<style>.boc{
    width: 200px;
    margin: 100px auto;
}
*{
    margin: 0;
    padding: 0;
}
.box{
    width: 150px;
    height: 40px;
    line-height: 40px;
   
    background-color: #b6b9c7;
    border: 1px solid black;
}
ul{
    width: 150px;
    border: 1px solid black;
    list-style: none;
}
li{
    width: 100%;
    height: 20px;
    background-color: #e0e2eb;
    border-bottom: 1px solid white;
    
}</style>
<body>
    <div class="boc">
        <div class="box">播放列表...</div>
        <ul>
           <li>歌单1</li>
           <li>歌单2</li>
           <li >歌单3</li>
           <li>歌单4</li>
           <li>歌单5</li>
        </ul>
    </div>
</body>
<script>
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    var uuu=document.querySelector('ul')
    var box=document.querySelector('.box')
    box.onclick=function(){
        if(uuu.style.display=='block'){
            uuu.style.display="none"
        }else{
            uuu.style.display='block'
        }
    }
    for(var i=0;lis.length;i++){
        lis[i].onmousemove=function(){
            this.style.backgroundColor='white'
        }
        lis[i].onmouseout=function(){
            this.style.backgroundColor=''
        }
    }
</script>
</html>